There are correct and incorrect ways to fuse Pokémon.

Fusion Dance [ COMIC ]

If you’re completely new to the whole Pokémon fusion thing, go here and play around for a little bit. It’s a lot of fun.

And then, when you’re done with that, head on over to SMOSH and see 25 incredible pieces of art based on Pokémon fusions. There’s a lot more good examples than just those on the internet, but it’s a good starting point.